1. Field of the Invention
The present invention relates generally to the field of automated sensing systems and methods. More specifically, the present invention is directed to systems and methods for detecting the presence and/or absence of a solid, liquid or gas utilizing an RF energy emitter and RF energy detector for determining whether a solid, liquid or gas is present within a defined physical space between the RF energy emitter and RF energy detector.
2. Description of the Related Art
A wide variety of conventional systems and methods are available for determining whether a solid, liquid or gas is present within a specified physical space. For example, conventional detectors include such devices and techniques as mechanical fluid level sensors, product sensors and counters. Conventional systems utilizing mechanical sensors for fluid level detection often employ a float mechanism and a related sensor or visible indicator for identifying a location of the mechanical float or liquid level. One problem associated with conventional sensing systems and methods which rely upon mechanical structures or floating bodies for determining fluid level is that they are subject to mechanical breakdown as a result of corrosion and/or fouling of the mechanical float structure with debris and/or mineral or chemical deposits. In alternate approaches which rely upon a fluid level sensing channel, the channel itself is subject to corrosion and/or fouling with debris and/or mineral or chemical deposits.
In many vending and other similar dispensing applications there is a need to know when the system has run out of product. One of these applications is in the beverage industry. Specifically, for example, in post-mix beverage dispensers where it is desired to know when the bag of the concentrated liquid beverage is out of product there may be a need to sense fluid levels and/or the presence or absence of the product. Currently, in typical conventional post-mix dispensers, a vacuum sensor is typically used to detect when the concentrate liquid bag is out of product. This method has numerous disadvantages;                The sensor must come into contact with the beverage concentrate liquid;        It works only for systems where the concentrated liquid dispensing pump is powerful enough to create a vacuum, when the bag is out of product, and trigger the sensor.        It has a long response time during which water is dispensed.        
A second method that is used to detect if the concentrated liquid bag is out of product relies upon the use of one or more electrode pairs and measurement of the electrical conductivity or resistance between the electrodes for the purpose of sensing fluid level or the presence and/or absence of the fluid at a particular level. This method also has the disadvantage that it is necessary to have the two electrodes come in contact with the concentrated liquid and if the electrodes are not kept clean, the sensor will malfunction.
Yet another conventional approach relies upon the use of an optical sensor. However, this technique will not work when the tubing through which the product travels is opaque, or when the liquid leaves residue on the inner walls of the tubing thereby blocking the sensor light. Also, most of the Silicon or Tigon tubing that are used reflects or absorb most of the sensor infrared light and the sensitivity and resolution of devices which rely upon this technique is therefore very poor. Furthermore, the performance of optical sensors can be degraded by the presence of debris, which is often encountered in packaging and manufacturing environments. For example, in the pharmaceutical industry dust from the tablets can cause erroneous readings from optical sensing devices.
Accordingly, typical conventional mechanical, optical or electronic sensors for detecting the presence of a liquid in implementations for vending machines such as coffee dispensers and the like are inherently prone to degradation and breakdown and there remains a need for improvement or replacement of these conventional devices. Mechanical floating structures have been used for sensing fluid levels in a wide variety of devices including automated dispensers for coffee and other liquids as well as fuel tanks and ink tanks. Mechanical sensors have also been used in a wide variety of applications such as, product detectors and counters including solid pharmaceutical product sensors and counters. All of these known conventional mechanical systems for detecting the presence of a solid, liquid or gas are subject to degradation in performance over time as a result of the mechanical breakdowns noted above.
More recently, other conventional approaches for sensing the presence and/or absence of a solid, liquid or gas include the use of ultrasonic detectors for making the determination of whether a solid, liquid or gas is present. One shortcoming of these conventional systems is that an ultra sonic detector for a solid, liquid or gas requires a complicated emitter and detector structure as well as a complex signal analyzer for examining the returned signal. Accordingly, although this approach is not necessarily subject to the mechanical breakdown problems associated with conventional mechanical sensors for determining the presence of a solid liquid or gas, this alternate conventional technique has its own shortcomings and requires a significant economic expenditure for the manufacture of the ultrasonic detecting system. Furthermore, ultrasonic detectors are not very suitable for use as a detection mechanism when there is an air gap between the product to be detected and the ultrasonic emitter.
Accordingly, there remains a need in the field for an accurate and reliable system and method for detecting the presence of a solid liquid or gas which is not subject to the potential breakdowns associated with conventional mechanical devices and is relatively inexpensive compared with the known ultrasonic techniques for sensing the presence of a solid, liquid or gas.